This invention relates to molding apparatus, and more particularly to improvements in injection molding apparatus of the plural-cavity type.
In the fabrication of end closures for containers it has been a practice to form, by an injection molding operation, a closure sealing ring along a peripheral region of a metal disk insert comprising a central portion of the closure. In such a molding operation, an insert is placed in a suitably formed mold cavity followed by injection of the molding compound to form the sealing ring. Closures of this type are, of course, mass produced at relatively high rates of speed, using multiple cavity injection molding apparatus. The quantity of molding compound typically is metered according to the volume required to fill all the cavities, assuming a closure insert is present in each cavity. Malfunctions sometimes occur, however, resulting in that one or more inserts are missing from the mold. Injection of the molding compound under this condition wastes it on a cavity from which an insert is missing, and forms a defective sealing ring about any insert that is present.
It is a general objective of the invention to provide improved multiple-cavity injection molding apparatus overcoming the hereinabove stated difficulties.
It is a further and more specific objective of the invention to provide novel means for metering flow of molding compound into a multiple cavity mold according to the number of inserts present in the individual cavities.
It is a further objective of the invention to provide improved means for controlling the supply of molding compound in an injection molding apparatus.